This invention relates generally to plethysmographic measurement of human body composition. More specifically, the present inventions relate to apparatus and methods for plethysmographic measurement of body composition for infant subjects.
The assessment of body composition, including measurement of fat and fat-free mass, provides physicians with important information regarding physical status. Excess body fat has been associated with a variety of disease processes, such as cardiovascular disease, diabetes, hypertension, hyperlipidemia, kidney disease, and musculoskeletal disorders. Low levels of fat free mass have been found to be critically adverse to the health of certain at-risk populations, such as infants and the elderly.
Similarly, particularly with respect to infants, body weight has been shown to be useful as a diagnostic measurement for the assessment of physical status. Disturbances in health and growth, regardless of origin, almost always affect body weight in newborns and infants. In particular, for very low birth weight infants, weight and weight gain patterns are relevant both in determining infant energy needs and in evaluation of health progression and physical development.
A variety of methods are currently used in the assessment of body composition. One common method is a skin fold measurement, typically performed using calipers that compress the skin at certain points on the body. While non-invasive, this method suffers from poor accuracy on account of variations in fat patterning, misapplication of population specific prediction equations, improper site identification for compressing the skin, poor fold grasping, and the necessity for significant technician training to administer the test properly. Moreover, no successful methodology for determining infant body composition using skinfold measurement has been devised.
Another method employed is bioelectric impedance analysis (xe2x80x9cBIAxe2x80x9d). Bioelectric impedance measurements rely on the fact that the body contains intracellular and extracellular fluids that conduct electricity by passing a high frequency electric current through the body, BIA determines body composition based on the bodies"" measured impedance in passing current and known impedance values for human muscle tissue. However, this method can be greatly affected by the state of hydration of the subject, and variations in temperature of both the subject and the surrounding environment. Moreover, BIA has not been successfully applied with infant subjects.
The most common method used when precision body composition measurements are required is hydrostatic weighing. This method is based upon the application of Archimedes principle, and requires weighing the subject on land, repeated weighing under water, and an estimation of air present in the lungs of the subject using gas dilution techniques. However, hydrodensitometry is time consuming, typically unpleasant for the subjects, requires both significant subject participation and considerable technician training and, due to the necessary facilities for implementation, is unsuitable for clinical practice. Further, the application of hydrodensitometry to infant populations is precluded by the above concerns.
One technique offering particular promise is performing body mass measurement is the use of plethysmography. Plethysmographic methods determine body composition through application of Boyle""s law to the differentiation in volume between the volume of an empty measurement chamber, and the volume of the chamber with the subject to be measured inside. Examples of this technique are disclosed in U.S. Pat. No. 4,369,652 issued to Gundlach, U.S. Pat. No. 5,450,750 issued to Adler, U.S. Pat. No. 4,184,371 issued to Brachet, and U.S. Pat. No. 5,105,825, issued to Dempster. This procedure, in contrast to hydrodensitometry, does not cause anxiety or discomfort in the subject, and due to the ease and non-invasiveness of the technique, can in theory be applied to infant subjects for whom hydrodensitometry is impractical.
However, conducting plethysmographic body measurement of infants using current plethysmographic chambers has proven to be impractical. Current plethysmographic chambers are not sized for infants. Given the lower body mass measurements of infant subjects, even more precise determination of chamber volume is required than for adults if such present chambers were to be used. Further, present chambers require the subject to be measured to remain in a seated position within the chamber during measurement, which is not feasible for use with infant subjects.
In view of the foregoing, it would be desirable to provide a plethysmographic chamber for measurement of infant body composition.
It would further be desirable to provide a system which integrates other useful diagnostic measurements, such as determination of body weight, in a plethysmographic measurement chamber for infants.
In view of the foregoing, it is an object of the present invention to provide a plethysmographic chamber for measurement of infant body composition.
It is another object of the present invention to provide a system which integrates other useful diagnostic measurements, such as determination of body weight, in a plethysmographic measurement chamber for infants.